Abstract: DOI: 10.4149/BLL_2022_065 Bratisl Med J 2022; 123 (6) 421 – 427 CLINICAL STUDY Is there a relationship between vitamin D levels, inflammatory parameters, and clinical severity of COVID-19 infection? OZTURK Gulcan1, ERASLAN Berrin Zinnet2, AKPINAR Pinar1, KARAMANLIOGLU SILTE Duygu1, OZKAN UNLU Feyza1, AKTAS Ilknur1 Department of Physical Medicine and Rehabilitation, University of Health Sciences Fatih Sultan Mehmet Education and Training Hospital, Istanbul, Turkey. drgul_can@hotmail.com ABSTRACT OBJECTIVES: This study is aimed to determine the relationship between 25-OH vitamin D levels, inflammatory parameters of neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), c-reactive protein (CRP) levels and the disease severity of COVID-19 infection. BACKGROUND: Inflammation plays a key role in the pathogenesis of COVID-19 while identifying the clinical course and prognosis. The effect of vitamin D deficiency on contribution to inflammation in COVID-19 is unclear. METHODS: Based on the classification of the clinical course of COVID-19, the patients were divided into three groups, i.e., with mild (Group 1), moderate (Group 2) and severe/critical cases (Group 3). The 25-OH vitamin D values were defined as deficient, insufficient or normal. RESULTS: There were no statistically significant differences in the distribution rates of 25-OH vitamin D levels (p>0.05) between the groups. Inflammatory parameters in Group 3 were statistically significantly higher as compared to Groups1 and 2 (p < 0.05). Multivariate logistic regression analysis revealed that NLR was an independent predictor of disease severity. CONCLUSION: There is no relationship between the severity of COVID-19 infection and 25-OH vitamin D deficiency. Inflammatory parameters are associated with the disease severity, while NLR is an independent predictor of severe COVID-19. There was no correlation between 25-OH vitamin D and inflammatory markers (Tab. 4, Fig. 1, Ref. 38). Text in PDF www.elis.sk KEY WORDS: COVID-19 pandemic, severity of illness, inflammation, vitamin D.